1. Field of the Invention
The present invention relates to a radiation-sensitive resin composition. More particularly, the present invention relates to a radiation-sensitive resin composition suitably used as a chemically amplified positive-tone resist useful for microfabrication using ultraviolet rays, far ultraviolet rays, X-rays, and various other types of radiation such as charged particle rays.
2. Prior Art
In the field of microfabrication represented by the manufacture of an integrated circuit device, design rules for the lithographic process have been rapidly miniaturized in order to achieve a higher circuit integration. In recent years, a lithography process in which microfabrication of line width of 0.5 .mu.m or less can be carried out stably and with higher accuracy has been positively developed.
However, according to conventional methods using visible rays (wavelength: 700-400 nm) or near ultraviolet rays (wavelength: 400-300 nm), it has been difficult to form such a fine pattern with precision. Because of this, a lithography process using shorter wavelength radiation (wavelength: 300 nm or below), which ensures a wider depth of focus and finer dimensions for design rules, has been proposed.
As a lithography process using such shorter wavelength radiations, a method using far ultraviolet rays such as a KrF excimer laser (wavelength: 248 nm) and ArF excimer laser (wavelength: 193 nm) and a method using X-rays such as synchrotron radiation or charged particle rays such as electron beams have been proposed. In addition, International Business Machines Corporation (IBM) has proposed a "chemically amplified resist" as a high resolution resist corresponding to these shorter wavelength radiations. Up until the present, development and improvement of the chemically amplified resist has been energetically pursued.
A photoacid generator contained in the chemically amplified resist generates an acid on exposure to radiation, and the acid acts as a catalyst to cause chemical reactions such as alteration of polarity, cleavage of a chemical bond, and crosslinking reaction in the resist film to form a resist pattern by utilizing the change in solubility of the exposed part in a developer.
As a conventionally proposed chemically amplified resist exhibiting relatively good performances as a resist, the following resists have been proposed: a resist using a resin in which an alkali affinitive group in an alkali-soluble resin is protected by a t-butyl ester group or a t-butoxycarbonyl group (Japanese Patent Publication No. 27660/1990); a resist using a resin in which an alkali affinitive group in an alkali-soluble resin is protected by a ketal group (Japanese Patent Application Laid-open No. 140666/1995); and a resist using a resin in which an alkali affinitive group in an alkali-soluble resin is protected by an acetal group (Japanese Patent Application Laid-open No. 161436/1990 and No. 249682/1993).
However, it has been pointed out that these chemically amplified resists have respective characteristic problems, whereby the practical use is accompanied by various difficulties.
One of the fatal problems is irregular line widths of the resist pattern or a T-shaped resist pattern due to the time delay (Post Exposure Time Delay, hereinafter called "PED") between irradiation and the bake process (hereinafter called "post-bake").
In addition to the above problem, because resolution, bake temperature, and the like are highly dependent on the PED, process stability becomes insufficient, whereby further improvement of the overall characteristics of the chemically amplified resist has been required.
Among the above chemically amplified resists, a positive tone resist comprising a copolymer of hydroxystyrene and t-butyl acrylate as the resin component (hereinafter called "type 1") and a positive tone resist containing a resin in which a phenolic hydroxyl group of a poly(hydroxystyrene) is protected by a ketal group or an acetal group (hereinafter called "type 2") have proposed as resists which overcome the above problems to some degree.
However, because the resist of the type 1 contains an acrylic component whose absorption coefficient is small at a wavelength of248 nm, the effect of swing curves becomes greater, thereby exhibiting an impaired pattern profile and inferior resolution. Moreover, the resist of the type 2 exhibits lower heat resistance, giving rise to impaired pattern profiles. As described above, these resists can not satisfy properties such as high resolution and superior heat resistance, which have been required for the recent increasing demand for microfabrication.
The present invention has been achieved in view of the above situation, and, in particular, as a result of considering a resin component which constitutes a chemically amplified resist in more detail. The object of the present invention is to provide a radiation-sensitive resin composition suitably used as a chemically amplified positive tone resist which is sensitive to various types of radiation and exhibits excellent sensitivity and resolution, fewer effects from swing curves, excellent pattern profile, and superior heat resistance.